The allegations against Alexander Smirnov, 43, were outlined in new Department of Justice filings in the case on Tuesday.

Mr Smirnov is accused of lying when he claimed bribes were paid to the Bidens via a Ukrainian energy firm, Burisma.

He was charged last week with giving false statements to the FBI.

Mr Smirnov's claims were part of an ongoing effort by Republicans to impeach President Biden.

He was arrested in Las Vegas, Nevada, on Thursday after returning from an overseas flight, the justice department said.

Prosecutors had asked for Mr Smirnov, a dual US-Israeli citizen, to be held without bail, arguing that he has no ties to Las Vegas, but does have contacts with Russian intelligence agencies.

But on Tuesday US Magistrate judge Daniel Albregts allowed the defendant to be released from custody and be monitored by GPS until his trial. He must remain in Nevada's Clarke County and is banned from applying for a new passport.

Mr Smirnov - who had been held at a jail in Pahrump, about an hour from Las Vegas, since his arrest - did not speak to journalists as he left court.

The justice department says that he disclosed his intelligence contacts to his FBI handler, saying he could use those connections - which prosecutors described as " extensive and extremely recent" - to leave the US.

In court documents filed Tuesday, prosecutors also alleged that Mr Smirnov told authorities he had only $1,500 in cash and $5,000 in a bank account, when in reality he had access to about $6m in "liquid funds".

"The fact that Smirnov misrepresented his assets alone should cause Smirnov to be detained because it shows that, at the first opportunity, he did not provide true and complete information to pretrial services," the filing says.

In December 2023, the legal filing says, Mr Smirnov attended an overseas meeting with "a high-ranking member of a specific Russian foreign intelligence service".

Mr Smirnov told his FBI handler that he learned Russian intelligence had intercepted "several" phone calls made at a certain hotel by prominent US people, according to the justice department. Neither the hotel nor its location is specified.

Mr Smirnov allegedly said the eavesdropped recordings could be used as "kompromat" (compromising material) during the 2024 election campaign.

He was charged by Special Counsel David Weiss - who has overseen the investigation of Hunter Biden - with providing "false derogatory information" to the FBI about the president and his son in June 2020.

Prosecutors allege that Mr Smirnov was motivated by his dislike of the president.

If convicted, he faces a maximum of 25 years in prison.

In a separate court filing on Tuesday, Hunter Biden's attorneys sought to have federal tax charges dismissed, arguing that he was the victim of politically motivated "selective and vindictive prosecution".

Additionally, the filings argue that the prosecutors' assertions that the younger Mr Biden lived a "lavish" and "extravagant" lifestyle were "irrelevant and prejudicial" to the case.

By Mike Wendling